Study On Evaluation Method Of Compost Maturity By Germination Index

At present,aerobic composting technology is widely used in the resource treatment of livestock and poultry manure,which has the advantages of large processing capacity,simple operation,and low operating cost.The degree of compost maturity,a product of aerobic fermentation,has an important effect on the utilization of compost products.Before the compost product is officially applied to the farmland,compost maturity is assessed to prevent the immature compost product from entering the farmland and affecting the growth of crops.Germination index（GI）is one of the main methods for evaluating compost maturity at domestic and overseas,but the correlation between GI and physical and chemical indexes,microbial community abundance and metabolic differences of compost was not clear,which restricted the popularization and application of GI.Therefore,it is of great theoretical and practical significance to standardize the GI method and explore its relationship with physical and chemical properties of materials,abundance of microbial community and metabolic difference substances during the process of composting.In this study,based on summarizing the previous work,using fresh pig manure as compost raw material,crushed wheat straw as conditioner,and self-made forced ventilation aerobic composting reactor,the mixed material was subjected to aerobic composting for 42 d.In the composting experiment,the operation method of germination index was explored,and the relationship between basic physical and chemical properties of compost,microbial community abundance,metabolic differences and germination index was studied.The specific research results are as follows:（1）In the GI operating procedures,the seeds of the GI should be radish seeds,and the number of seeds should be 10.The ratio of compost sample to distilled water should be configured according to the solid-liquid ratio of 1:10,and the oscillation frequency of the extract preparation is 100 rpm,the pretreatment of the extract is selected for static filtration.The incubation temperature was 25 ^oC and the incubation time was 48 h.（2）There was a significant negative correlation between the physical and chemical indexes of composting and GI.Electric conductivity（EC）was significantly negatively correlated（p<0.05）,ammonium nitrogen（NH₄⁺-N）,organic matter（OM）,acid exchangeable state of copper（F1）,easily reduced state of copper（F2）and acid exchangeable state of zinc（F1）were Extremely significant negative correlation（p<0.01）.Available phosphorus（AP）,available potassium（AK）,total potassium（TK）,total phosphorus（TP）,nitrate nitrogen（NO₃^--N）,total copper（Cu）,total zinc（Zn）,zinc reducible state（F2）showed extremely significant positive correlation（p<0.01）.（3）There was a correlation between the abundance of microbial community and germination index.In bacteria,the abundance of Ruminofilibacter,Nonomuraea,Thermopolyspora,Limnochorda,Thermomonospora,Longispora were positively correlated with germination index;The abundance of Stenotrophomonas,Pseudomonas,Acinetobacter and Proteiniphilum were negatively correlated with the germination index.In fungus,the abundance of Melanocarpus,Humicola,Hydropisphaera,Mycothermus and Iodophanus were positively correlated with germination index;The abundance of Sporobolomyces,Blumeria and Pseudobensingtonia were negatively correlated with germination index.（4）The composition of the compost material changed greatly before and after the aerobic composting fermentation.Through metabolomic analysis,a total of 1178 metabolic differences were detected,mainly divided into lipids and lipid-like molecules,benzenoids,organic heterocycles compounds,organic acids and derivatives,phenylpropanoids and polyketides,etc.,Involved in metabolic pathways are mainly Neuroactive ligand-receptor interaction,Biosynthesis of alkaloids derived from shikimate pathway,Degradation of aromatic compounds,Nicotinate and nicotinamide metabolism,Methane metabolism,Biosynthesis of plant secondary metabolites,Steroid hormone biosynthesis,Biosynthesis of alkaloids derived from histidine and purine,Biosynthesis of unsaturated fatty acids,etc.,Among the metabolites,ferulic acid,gentisic acid,protocatechuic acid,resorcinol,kinetin,trigonelline,pyrogallol,allantoin,methyl palmitic,p-coumaric acid,camptothecin,palmitic acid and indole-3-butyric acid may affect the germination index of compost.In summary,the basic physical and chemical properties of compost,microbial community abundance,metabolic differences and germination index are all correlated.During the composting process,the relevant parameters can be adjusted according to needs to obtain high-quality,low phytotoxicity organic fertilizers.